The aim of this study is to evaluate the therapeutic efficacy and safety of MDX-H210 in combination with GM-CSF in patients with metastatic or locally advanced and unresectable HER2/neu positive colorectal carcinoma. In addition, the pharmacologic effects of this combination on various components of the immune system will be assessed. The specific aims are: 1) to obtain a preliminary assessment of therapeutic benefit as measured by anti-tumor effects, by MDX-H210 combined with GM-CSF in colorectal cancer patients; 2) to evaluate the safety and tolerance of the MDX-H210/GM-CSF regimen in colorectal cancer patients; and 3) to determine immunologic effects of MDX-H210 in combination with GM-CSF. This protocol is a Phase II study in patients with advanced colorectal cancer. Patients will receive an intravenous infusion of BsAB on cycle days 3,7,and 11 and a subcutaneous injection of GM-CSF on cycle days 1 through 14. Physical examination and laboratory testing will be used to monitor patient safety and toxicity. In selected patients BsAb binding to tumor target tissue and immunologic assays will be performed.